1. Field of the Invention
The present invention relates generally to the field of communications systems. More specifically, the present invention relates to communication systems in which electronic information is transmitted in packets.
2. Background
Communications systems may be subject to intermittent, random bursts of noise, often referred to as burst noise or impulse noise. This burst noise can result in the introduction of errors into the electronic information transmitted over the communications system. For example, in a communications system in which voice, data and/or other electronic information is transmitted in packets, the presence of burst noise can cause packets to become corrupted. Packet errors must be detected in order for a communications system to operate reliably. Where packet errors are detected but cannot be corrected, bad packets must be dropped and re-transmitted, resulting in a net loss of transmission speed and network bandwidth. If the dropped packets include voice information, the result may be a loss in overall quality of service (QOS).
Some communications systems utilize Forward Error Correction (FEC) and/or interleaving in order to control errors in transmitted data resulting from burst noise. FEC involves the addition of extra information to data before it is transmitted, which is then used by the receiver to detect errors and correct the data when necessary. Depending on the FEC algorithm used, the receiver can detect and correct fewer than a predetermined number of errors per packet. Different types of FEC methods include block codes, cyclic codes, Reed-Solomon codes, and convolutional codes. Interleaving involves rearranging data to be transmitted according to a mapping and then returning the data to its original order at the receiver. Interleaving serves to spread the effects of burst noise over multiple packets, thereby decreasing the average number of errors per packet. This, in turn, enhances the ability of FEC to detect and correct errors.
For example, in a conventional cable modem system operating in accordance with DOCSIS (Data Over Cable System Interface Specification), the upstream physical (PHY) layer utilizes a combination of Reed-Solomon coding and interleaving to control errors. These methods allow an upstream receiver to correct errors resulting from burst noise of a certain duration and frequency of occurrence. However, there may be extreme cases where the burst noise is so severe that more errors are introduced into a packet than these combined methods can detect and correct. In these instances, packets will be lost. Therefore, what is needed is a technique for detecting and correcting packet errors in cases where burst noise is more severe than can be handled by conventional PHY technology.